This invention relates to stents, and in particular, to a method and apparatus for securely mounting a stent on a balloon catheter.
It is well known that a balloon catheter is well suited for use as a delivery and implantation system for an expandable stent. Typically, the stent is mounted over a balloon at the distal end of the catheter and is carried into a treatment zone through a blood vessel. Once properly positioned in the treatment zone, the balloon is inflated to expand the stent radially to open an occlude passage in the vessel caused by plaque or an aneurism. The catheter, during insertion, must oftentimes travel a rather tortuous path before reaching the treatment zone. If the stent is not securely mounted upon the balloon it can become dislodged or misaligned thus rendering the procedure ineffective. In severe cases, the stent may become entirely dislodged from the catheter while it is inside the patient, thus requiring its recovery through surgical procedures.
In an effort to more securely mount a stent upon a balloon catheter, it is common practice to compress the stent inwardly using special crimping tools similar to pliers. Because the crimping forces are applied repeatedly in different localized regions about the stent, the holding force around the stent tends to be non-uniform which can adversely effect the way the stent expands as the balloon inflates, thus leading to less than satisfactory implantation. More importantly, because the amount of force applied during the crimping operation is generally unregulated, the stent can penetrate the balloon rendering it uninflatable. The fact the balloon has been punctured by the stent generally is not discovered until such time as the stent has been positioned in the body. As a result, the catheter and stent must be retrieved from inside the patient and the procedure repeated.
Cylindrical crimping devices have also been devised wherein the balloon with a stent mounted thereupon are drawn into a cylinder having a predetermined inside diameter. The inside diameter of the cylinder is selected so that ideally the stent is collapsed just enough to apply a non-damaging, yet secure gripping force upon the balloon. This ideal relationship unfortunately is difficult to achieve in practice and puncturing of the balloon by the stent is not uncommon. Accurately guiding the stent bearing balloon into the cylinder can also be difficult and the stent may become misaligned or dislodged during this procedure.